1. Field of the Invention
The invention relates to the use of polyvinyl isoacetals, which are obtainable by reacting polyvinyl alcohol with branched aliphatic aldehydes, in formulations for printing inks.
2. Background Art
The use of polyvinyl acetals, in particular polyvinyl butyrals, as binders in printing ink formulations has long been known.
For this purpose, polyvinyl acetals which exhibit minimal viscosity in solution are often used (for example as binding agents in flexographic printing inks). At the same time it is thus possible to achieve a high content of pigment and binding agent in the printing ink, which then leads to a desired high intensity of colour.
During the production of such polyvinyl acetals, a correspondingly low-viscosity polyvinyl alcohol is normally selected as a starting material and is then acetylated, normally with n-butyraldehyde. Drawbacks of this approach include the tendency towards decreasing conversion rates and difficulties in the production of the product owing to the low glass transition temperature, which accompanies the low molecular weight, and the increasing tackiness associated with this. The low Tg (<65° C.) typical of low-viscosity polyvinyl acetals can also lead to difficulties in the end application, such as when printing the inks.
Many chemically different polyvinyl acetals have already been proposed for use in printing inks. It is thus known to use copolymers of tertiary vinyl esters with vinyl acetate as a starting material for the production of polyvinyl acetals, these copolymers comprising tertiary ester functions as impurities in the molecule. It is further known, in addition to butyraldehyde, to use long-chain aldehydes containing 5 to 10 carbon atoms for acetalation. Long-chain molecules such as sugar or oligoglycols can also react with the polymer chain, either after or during acetalation, and also act as impurities.
A drawback of these methods is the high complexity and the considerably higher costs compared to the acetalation of polyvinyl alcohol with butyraldehyde, which is established on an industrial scale.